The ability to measure the position of a mobile electronic device opens up a wide range of new applications. Applications that depend on location include location-based services, location-based advertising, context-aware computing, enhanced position determination (e.g., global positioning system—“GPS”), enhanced “911” and similar emergency response services, asset tracking and real-time location services, autonomous robotic systems, advanced man-machine interfaces, and assistive technologies for the disabled.
The availability of mobile electronic technology has substantially increased over the past decade. Cell phones, for example, have essentially saturated the market in the most developed countries. The proliferation of cell phones has introduced problems in the delivery of emergency services such as responding to “911” emergency calls due to the fact that cell phones are difficult to locate geodetically with sufficient accuracy. The U.S. Federal Communications Commission (“FCC”) has mandated that enhanced 911 services be supported by the cellular telephone infrastructure, but the providers of cell phone services are limited by the technology capability of their networks, and are presently able to locate individual cell phones to within a range of about 50-300 meters of the actual phone location. In a dense urban environment, such precision is insufficient to properly locate a 911 caller. Despite the crude precision of the cell phone positioning, social networking has emerged as a new location-based service delivering revenue for the cell phone service providers.
The commercialization of the United States Armed Services GPS allowed this infrastructure to support the positioning of mobile electronic devices by calculating the distance between the device and at least four low earth orbit satellites in the constellation of GPS satellites. The emergence of handheld GPS receivers created applications for GPS location services. The key limitation of GPS is that it is unable to deliver position information inside buildings. Enhanced GPS has emerged as a new technology direction as innovators seek to extend the functionality of GPS to the indoors. This has created the need for new infrastructure known as indoor, or in-building, positioning systems.
In the Enterprise Resource Planning sector, a technology known as Radio Frequency Identification, or RFID, has become an essential part of supply chain management systems that promote the tracking of inventory and assets in the business. The idea behind RFID is that relatively cheap, “smart” tags are used to identify goods and/or assets and a sophisticated RFID system is used to locate and identify the smart tags for tracking purposes. For many companies, location-aware technology is conferring competitive advantage in the marketplace.
One of the newest markets for location aware services is in the area of online advertising. Companies such as Google, Inc., Yahoo, Inc. and Microsoft, Inc. are aggressively competing in this field. By introducing information concerning target recipient location into online advertising, the value of an online ad can be greatly increased. Location based advertising promises to become the next front in the battle for online advertising market share.
Context aware computing is yet another technology that has been promoted by the large computing manufacturers and stimulated a great deal of R&D in computer science, engineering, and industry. As computing becomes increasingly mobile, the day will come when all computing will become location aware.
Market analysts have been predicting that location based services will be a multi-billion dollar market, but the timing of this prediction has been problematic. The problem is that, as technology becomes increasingly pervasive, consumers are becoming more aware and concerned about issues such as privacy. If there is any piece of personal information that would be viewed by the consumer as sensitive, the ability of an all-pervasive technology to track an individual's position would rank near the top of the list of concerns.
Contemporary suppliers of location based services have a wide range of technology on which such services are based. Positioning technologies use detectors based on light or sound. Technologies using light include optical detectors, radio frequency detectors, and infrared detectors, which are all special cases using the electromagnetic spectrum. Sound waves can also be used with systems using ultrasound at frequencies outside the range of human hearing above 20 KHz.
Technology suppliers have been attempting to enable improved context-aware computing by improving the resolution of location measurement systems. The state-of-the-art at present seems to be location resolution in the range of 1-10 meters. Expensive systems are available that can locate to fractions of a centimeter, but such systems cannot be deployed as part of a more pervasive location aware infrastructure.
In addition to the technology used (light or sound), there is also the methodology employed to determine position that determines the effectiveness of the method. Two methods of determining position common in the present market are time (or time difference) of arrival techniques (“TOA” and “TDOA”) and received signal strength indication (“RSSI”). TOA and TDOA allow calculating the position of a mobile electronic device by measuring the range from a transmitter to a multiplicity of receivers using timing electronics and knowledge of the speed of electromagnetic energy (or sound) through air. By determining the range between the transmitter and at least three independently positioned receivers, the three dimensional position may be calculated using trilateration. In the more general problem of locating a mobile device, GPS uses multilateration to calculate the position of a mobile GPS receiver. Four satellites are needed because there are 4 unknowns in the GPS problem, three values for the position (X, Y, Z) and one value for time.
For indoor position determination, TDOA systems require a multitude of receivers scattered through the surveillance volume. The cost of such systems is relatively higher as at least three receivers must be within range of the client device (the device to be located) and such receivers need to be networked together, independently powered, individually calibrated, etc. Deploying such infrastructure is cumbersome because overhead costs scale with respect to the number of receivers.
Another positioning system that is being deployed uses RSSI. Technologies such as Wireless Local Area Networks (“WLAN” or “WiFi”) and Bluetooth have RSSI built in. The idea is that the proximity of a client device to a WLAN device can be inferred from signal strength of radio transmissions between the client and WLAN device. Using complex algorithms and learning networks, the rough position of the client can be inferred. The advantage of such systems is that the coverage of existing WLAN and WiFi network hubs is quite high and the incremental cost of implementing a positioning system on RSSI is very low. The disadvantage is that it doesn't make much sense to increase WLAN penetration beyond what is needed to provide basic connectivity. The accuracy of RSSI is not much better than 10 meters, or “room level.”
The ubiquity of location servers will be limited until the cost of individual location servers becomes as cheap as other mass market consumer devices. Further, it is not only the cost of the location servers that must be taken into account. The cost of implementing the corresponding client location hardware and software that will limit the adoption rate of this technology must also be considered. Issues such as the cost of deploying the location aware infrastructure, the cost of maintaining and calibrating the infrastructure and the delivery of value-added services on that infrastructure will all play a role in the growth of this market.
However, it is evident that the present resolution of location aware devices is not sufficient to fully enable or deliver the promise of context aware computing. A breakthrough technology is required with a resolution that is an order of magnitude better than the current state of the art. One such technology that is being positioned as potentially delivering new levels of accuracy is Ultra-Wideband (“UWB”), which promises resolutions of order 15 cm-1 m with a multiplicity of receivers approach. Basically, the UWB system uses very narrow pulses to increase the resolving power of the TOA/TDOA approach. In order to shape a very narrow pulse, very large bandwidth is required.
US Patent Application Publication No. 2006/0199534 A1 (Location System for Bluetooth Enabled Devices) by Smith describes a method, apparatus and system for tracking and locating Bluetooth enabled devices. In this application, a network of Bluetooth sniffers is used to locate “lost” devices and their owners. A “parent” device independently monitors received signal strength between itself and a “child” device. When the signal strength of the child drops below a certain level, the child is deemed by the parent to be lost and an alert is issued to the sniffer network by the parent. Upon receipt of the alert, the sniffer network is then engaged to locate the child device through paging for the child device throughout a network of Bluetooth capable sniffer devices. The location is determined by proximity to a particular sniffer device at a known location. The method of the Smith '534 publication provides room level resolution in locating a child device which is adequate for this “lost and found” application. The methodology used uses RSSI (received signal strength indication) as the underlying technology.
U.S. Pat. No. 6,819,286 B2 (Location Determination For Mobile Units) issued to Armbruster et al. describes a method for location determination using Bluetooth techniques within buildings, underground or within other structures. The method disclosed in the '286 patent uses a multiplicity of subsidiary units arranged in a geometric pattern within the surveillance volume. A minimum of three subsidiary units are needed to measure the range to a mobile device to determine its position through trilateration techniques. This method is essentially the time delay of arrival method and relies on timing circuits for its implementation. In addition, the subsidiary units are each independently deployed through the surveillance volume and must be individually powered and networked together. The overall accuracy of the method is strongly dependent on the latencies of communications between the mobile unit and each of the subsidiary units.
U.S. Pat. No. 6,745,038 B2 (Intra-Piconet Location Determination and Tomography) issued to Callaway et al. describes a novel technique for intra-piconet location determination and tomography using received signal strength indication (RSSI). In this invention, the range between two piconet devices is determined by analyzing the destructive interference between direct and reflected wavepaths. By examining the RSSI versus carrier-frequency curve and determining the frequency separation of the nulls, the range may be determined. In principle, the method is capable of determining the range with an accuracy between 2.62 cm and 1 meter. When the position of a reflector is located at the origin, a system of equations describing the relative ranges between devices in the piconet can be solved to determine the positions of each device. In two dimensions, range measurements between a minimum of five devices are needed for solution while, in three dimensions, seven independent range measurements are needed.
U.S. Pat. No. 6,717,516 (Hybrid Bluetooth/RFID Based Real Time Location Tracking) issued to Bridgelall describes a hybrid device that allows RFID tags to be identified and located using Bluetooth technology. A plurality of fixed devices is distributed over an area containing the items to be tracked. The fixed devices are operated as RFID readers to identify and locate items having RFID tags. The fixed devices are preferably distributed at distances corresponding to twice the range of the devices when operated as RFID readers. The location of the RFID tag is inferred by several methods. The first method cited is locating a mobile slave device to within a piconet cell by determining which of the fixed devices is associated with the slave device. The resolution of this method is 30 feet (10 meters), equal to the maximum range of a Class 2 Bluetooth device. A second method is described whereby the Bluetooth cell size is adjusted to equal the range of the RFID passive tag reading capability, which has a resolution of 12-15 feet (anticipated to increase in the future with advancing technology). Finally, in a particularly preferred example, range may be determined from the phase of the response signals and the phase may be determined at a plurality of frequencies to resolve phase ambiguities. The problem of locating the position of a mobile device is addressed through defining a directional antenna beam pattern to limit the RFID tag exposure to a narrow cone angle. By changing the beam direction through electronic or mechanical beam steering the angular position of the RFID tag may be determined.
US Patent Application Publication No. 2002/0180640 (Location Estimation in Narrow Bandwith Wireless Communications Systems) by Gilkes et al. uses the phase difference between a known stable reference signal and a known signal output by a plurality of wireless mobile communications devices (location markers) at several known locations to determine the location of a mobile wireless communications device transmitting in the ISM radio band. The phase of the 1 MHz signal transmitted by the mobile device allows the phase difference to be detected within the location estimation environment within 300 meters (the wavelength of the 1 MHz signal). The location markers measure the phase difference between the embedded signal (the 1 MHz bitstream output by the Bluetooth radio) and a 1 MHz sine wave frequency reference signal that is produced at a fixed location by a stationary reference oscillator and is distributed to the location markers by coaxial cable, modified Ethernet or latency-free wireless means. A system calibration procedure is required to determine a phase delay parameter that measures the propagation delay between the reference source and each location marker. A 1 MHz phase comparator measures phase to 0.001 cycles (6.2832 milliradians), yielding 30 cm resolution (11.8 inches) in the range measured between the location marker and the mobile device. The location solution processor uses information from at least 4 non-coplanar location markers and solves simultaneous equations derived from the Cartesian coordinates of the location markers and the differences between the relative times of arrival reported by the location markers.